Myofibromas are well described in the head and neck region, but differentiating them
from smooth muscle lesions is still difficult using smooth muscle immunohistochemical stains. This study
evaluated the usefulness of the Masson trichrome stain in differentiating myofibromas from smooth muscle
lesions in the head and neck region.
Methods: Samples of 11 oral myofibromas, two leiomyomas, one angioleiomyoma, and one smooth muscle
hamartoma were retrieved from our archives. Immunohistochemistry and Masson trichrome stains were
performed on tissue sections of these lesions.
Results: All 11 oral myofibromas, seven from male patients and four from female patients, were solitary
myofibromas. The patients’ mean age at diagnosis was 32.8 years. Oral myofibromas occurred most commonly
on the gingiva (four cases) and in the mandible (three cases). With the Masson trichrome stain, the smooth
muscle cell cytoplasm was stained red, while the collagenous fibrous tissue was stained blue. Myofibromas
and smooth muscle lesions demonstrated different characteristic patterns with the Masson trichrome stain.
Myofibromas were composed of a much more collagenous stroma intermixed with the spindle cells. Thick
fibrous bundles with random, irregularly intersecting angles were prominent in myofibromas. Smooth muscle
lesions showed only minimal delicate fibrous tissue surrounding the smooth muscle cells and in the septa
between the smooth muscle masses. On low-power view, red masses of smooth muscle tumor surrounded
by blue fibrous tissue were observed.
Conclusion: The Masson trichrome stain can be a useful tool to differentiate myofibromas from smooth
muscle lesions, but immunohistochemical methods to rule out other spindle cell lesions are still needed.